With the quick development and expansion of the liquid crystal display market, fast response, high contrast ratio and wide view angle are the main issues to improve the display quality. Fast response, high contrast ratio and wide view angle are critically required in large size monitors and television (TV) applications. At present, in-plane switching (IPS), multi-domain vertical alignment (MVA) and axially symmetric-aligned microcell (ASM) are the typical candidates for obtaining the high display quality in these areas.
The IPS concept was first published by R. A. Soref in Applied Physics Letters, vol. 22, p. 165 (1973) and Journal of Applied Physics vol. 45, p. 5466 (1974). In 1992, Kiefer et al in Japan Display '92 p. 547, extended the IPS operating principle to display devices. The IPS liquid crystal display (LCD) works as the electric field is applied in the transversal direction and the liquid crystal (LC) molecules are rotated in the same plane as shown in FIG. 1 of this application. The IPS structure in FIG. 1 comprises an analyzer layer 10, a liquid crystal layer 11 sandwiched between a top substrate 12 and a bottom substrate 13 positioned above a polarizer 14 through which a backlight 15 is directed. The rubbing direction is indicated by arrows 16 and 17. As a result, the IPS mode exhibits a wide viewing angle and high contrast ratio, while the response time is relatively slow at approximately 50 milliseconds (ms).
As shown in FIG. 2, Fujitsu Ltd. invented a super high quality MVA LCD published in SID Technical Digest, vol. 29, p. 1077 (1998), Fujitsu Science Technical Journal, vol. 35, p. 221 (1999), and typically as disclosed in U.S. Pat. No. 6,424,398 B1 in 2002. In FIG. 2, The chevron-patterned protrusions 21 and 22 are created on the upper and lower substrates to form multi-domain LCD cells in multiple independent directions. The devices provide a high contrast ratio higher than 300:1, view angle wider than 160 degrees, and a fast response of 25 ms. Since the horizontal gap between the upper and the lower protrusions must be less than 30 micrometers (μm) in order to obtain fast response time, the pixel alignment needs high precision. Thus, the design specification and preparation process are not easy and the aperture ratio is limited. In addition, the adopted LC materials are constrained to negative dielectric ones in order to realize the deformed homeotropic alignment effect in the voltage-on state.
The axially symmetric-aligned microcell (ASM) was developed by Sharp Corp. as disclosed in U.S. Pat. No. 6,014,188 in 2000 and published in the SID Technical Digest, vol. 26, p. 575 (1995), and SID Technical Digest, vol. 29, p. 1089 (1998) respectively. In the ASM mode, the liquid crystal alignment 30 shows spiral distribution and the polymer walls 31 are formed by ultra-violet (UV) exposure to construct microcell pixels 32 as shown in FIG. 3 of this application. The view angle of more than 120 degrees, high contrast ratio of 300:1 and a medium response time of 30 ms can be obtained in the ASM mode. Since the polymer network stabilizes the LC alignment in the microcells, the large-scaled precise control of the microcells and the long-term stability of them are the questionable problems for this mode.
In the above-mentioned modes, two linear polarizers are usually used. Recently, Iwamoto et al reported a MVA mode using circular polarizers in the 9th International Display Workshops, p. 85 (Hiroshima, Japan, Dec. 4–6, 2002). The light efficiency is improved. In the IPS mode, a rubbing process is necessary in order to achieve uniform LC alignment. The problems associated with the rubbing process are thin film transistor (TFT) damages, dust particle contamination, and static charges.
There is still a need to overcome problems with existing technology to obtain high quality displays for large monitors. As discussed above, IPS has a relatively slow response time and requires a rubbing process. MVA LCD has difficult design specifications, which results in a tedious preparation process. ASM requires precise control of the microcells and has problems with long-term stability. The present invention resolves many problems with current technology while providing a reliable, simple structure suitable for high yield mass production.